Multi Point Relays are nodes in wireless Ad-Hoc networks that do the job of relaying messages between nodes, they also have the main role in routing and selecting the proper route from any source to any desired destination node.
OLSR routing protocol : MPRs advertise link state information for their MPR selectors periodically in their control messages. MPRs are also used to form a route from a given node to any destination in route calculation. Each node periodically broadcasts Hello message for the link sensing, neighbor’s detection and MPR selection process. Each node can get topology up to 2 hops from Hello messages. The information about the symmetric one hop and two hops neighbors is used to calculate the MPR set. Each node selects set of neighbor nodes as MPRs from among 1-hop neighbors with symmetric link, which covers all the two, hop neighbors and records in MPR selector table. MPR is recalculated when a change in one-hop or two - hops neighborhood topology is detected. Every node periodically broadcasts list of its MPR selectors instead of the whole list of neighbors. Upon receipt of MPR information, each node recalculates and updates routes to each known destination. In order to exchange the topological information, the Topology Control (TC) message is broadcasted throughout the network. Only MPRs need to forward TC messages each node maintains the routing table in which routes for all available destination nodes are kept because of the proactive nature[1]